Intracranial pressure sensor

Abstract

An intracranial pressure device for measuring CSF pressure in a skull includes a housing located between the scalp and the skull containing pressure device circuitry and a conduit extending downwardly from the housing to the vicinity of the CSF. A pressure sensor is coupled to the conduit and located in communication with the CSF wherein the pressure sensor directly senses the pressure of the CSF and provides a signal representative of the pressure of the CSF to the pressure device circuitry by way of the conduit. The skull has a dura and the conduit extends by way of an opening through the skull and an opening through the dura to position the sensor in direct contact with the CSF. A fluid reservoir can be in communication with the CSF by way of a tube and by way of the housing. The fluid reservoir contains CSF.

Description

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT[0001]This invention was supported in part by funds from the U.S. government (NIH Grant R21 NS050590-01). The U.S. government may therefore have certain rights in the invention.FIELD OF INVENTION[0002]This invention relates to the field of physiological measurements and, in particular, to a system for measuring the presence of a fluid.DESCRIPTION OF RELATED ART[0003]The final common pathway for death and permanent disability in head injuries and brain disease is usually increased intracranial pressure. For this reason, measurement and control of intracranial pressure is a major focus of care in these cases, both acutely and chronically. It is known in the art to provide microelectromechanical (MEMS) based microwave intracranial pressure sensing devices which allow for non-invasive monitoring of intracranial pressure when used with a portable microwave monitor. Such devices are useful in several areas. However, existing n...

AI Technical Summary

Benefits of technology

[0032]The sensor can be attached to a probe-like extension that can extend from the vicinity of the scalp or the skull, through an opening in the skull, through the dura, and down to the level of the CSF. The probe can include a pressure sensor attached thereto and positioned to communicate directly with the CSF. The subdural sensor of the invention can thus directly sense the pressure of the CSF. Accordingly, the subdural sensor can provide a direct reading of the pressure of the CSF. A housing, such as a disc shaped housing, can contain the other elements of the intracranial pressure monitoring system, such as the battery and the electronics, and any other required components. The housing can be placed outside the skull, immediately below the scalp. In an alternate embodiment the housing can be place outside the scalp. The opening extending from the housing to the CSF can be very narrow, since it only needs to accommodate the sensor and the probe. For example, a diameter of 2-4 mm can be more than sufficient. The fact that only a very narrow opening through the skull and dura is required, and that only the probe needs to be extended through the opening, facilitates implanting the intracranial pressure monitoring system under adverse conditions.

[0033]Additionally, a battery and a system for keeping the battery charged can be provided. A flexible substrate can be implanted beneath the surface of the scalp. The implanted substrate can be provided with one or more energy transducers for converting light energy into electrical energy. The electrical energy from the energy transducers can trickle charge the batteries in the monitor. The energy transducers can be located on the outside of the scalp or implanted beneath the surface of the scalp. If they are implanted beneath the surface of the scalp they should not be implanted so deep that light cannot pass through the tissue to the energy transducers to be converted to electrical energy in order to charge the battery. Alternately, the electrical energy can be used to charge a capacitor that will run the device for a short duration of time, which is just enough to record the measurements from the device. Thus, the capacitor can eliminate the need for a battery. The energy transducers can be photodetectors, photodiodes, photocells, solar cells, etc. Additionally, in one embodiment the energy transducers can be coated with parylene. A coating layer of parylene having a thickness of about 2.5 microns does not substantially alter the efficiency of the energy conversion of the energy transducers.

[0036]Thus, a reliable and mass-producible MEMS-based microwave intracranial pressure sensing device for use with a portable microwave monitor and methods for non-invasively monitoring and controlling intracranial pressure with this device under adverse conditions are provided.

Problems solved by technology

However, existing neurosurgical intracranial monitors can typically be implanted and used only in hospital settings, most typically in operating rooms or intensive care units, and have limited useful life due to drift, infection and other factors.

Stroke is the third leading cause of death in the United States, and head injury is a leading cause of death in adolescents and young adults.

Since the skull forms an almost complete rigid container for the brain, measuring intracranial pressure directly can be very difficult.

However, penetration of the skull to insert a pressure sensor requires a neurosurgical procedure with significant risks.

Existing neurosurgical intracranial pressure monitors could only be used in the hospital setting, and have limited useful life due to drift and infection.

However, devices with significant inductive or magnetic components, including radio frequency circuit-based devices, were not compatible with magnetic resonance imaging, a procedure often critical to management of patients with abnormal intracranial pressure.

Further, many of these devices had a limited lifetime, particularly devices with plastic components, which age rapidly in vivo when in contact with extracellular space, or slide bearings, which are not reliable over long term.

For example, a device relying on measurement via a flexible diaphragm could become useless if encased in relatively stiffer scar tissue while a device requiring CSF flow could become prone to clogging in many cases.

In addition, many of these devices required either a large number of parts, precise machining or rare and / or exotic materials making manufacture and assembly cost prohibitive.

Accordingly, remote monitoring was not possible.

Further, these implants required large inductors, e.g. 3.7 microH (See DeHennis, A. and Wise, K. D. Digest of IEEE Conference on MicroElectroMechanical Systems, 2002, 252-255) and 150-200 nH (See Simons et al., Digest of 2004 IEEE International Microwave Symposium, 2004, 3:1433-1436), which are not compatible with magnetic resonance imaging.

Accordingly, there was a lack of stable, biocompatible, rugged and inexpensive intracranial pressure sensors sufficiently small to be inserted through the burr hole and left inside the cranium following most common neurological procedures, which were compatible with modern imaging techniques including, but not limited to CT, MRI and ultrasound and which monitored intracranial pressure.

The methods discussed by Meyerson breach the skull and have varying degrees of invasiveness.

Additionally, Meyerson addresses a drawback common to all of the foregoing methods, the need to calibrate the devices used in the techniques.

While the Meyerson system allows measurement of parameters related to intracranial pressure outside of a hospital environment, it does not directly measure the intracranial pressure or provide any means for controlling the pressure prior to the time the patient reaches the hospital.

However, the systems taught by Geocadin and Sood, like the preceding references, were not suitable for emergency implantation in a patient under adverse conditions such as the those existing at the scene of an accident or on a battlefield, in order to monitor and control intracranial pressure until more sophisticated facilities were available.

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